Apparent contralateral inferior oblique muscle overaction after unilateral inferior oblique muscle weakening procedures

Abstract

Background: Unilateral inferior oblique muscle weakening surgical procedures often lead to the appearance of inferior oblique muscle overaction in the contralateral eye. The purpose of this study was to determine how different types of unilateral inferior oblique muscle procedures affect the apparent function of the inferior oblique muscle in the contralateral eye. Methods: A computer search was performed to locate all patients on the pediatric ophtalmology service at the Wilmer Ophthalmological Institute who underwent a unilateral inferior oblique muscle weakening procedure from 1980 to 1994. Only patients with a diagnosis of primary inferior oblique muscle overaction were included in the study. Results: Fourteen patients met the inclusion criteria. One patient had undergone an anterior transposition of the inferior oblique muscle, seven patients had undergone a 10 mm recession of the inferior oblique muscle, and six patients had undergone a myectomy of the inferior oblique muscle. Before the operation, there was no difference in the inferior oblique muscle function of the contralateral eye among the three groups. However, after the operation apparent inferior oblique muscle overaction developed more frequently and to a greater degree in the contralateral eye among patients in the anterior transposition and 10 mm recession groups than among patients in the myectomy group. Conclusion: Either anterior transposition or 10 mm recession of the inferior oblique muscle may limit elevation in abduction in the eye on which inferior oblique muscle surgery was performed. The limitation of elevation in abduction may create apparent inferior oblique muscle overaction in the contralateral eye.